Epinephrine (adrenaline) is sometimes the best treatment for life-threatening allergies. The drug is stored in salt water in glass ampules, which are broken open when the drug is needed. The amount of epinephrine contained in the ampule label is usually expressed as both a dose (1 mg of the drug per 1 mL of salt water) and a ratio (1 part drug for every 1000 parts of salt water). Doctors understand doses much better than ratios. A ratio requires doing arithmetic to figure out how much drug to give. Dose errors with epinephrine are common. Having to do arithmetic to figure out how much epinephrine to give a person in an emergency might lead to those errors and to delays in giving the drug.